Circuit and a method for configuring pad connections in an integrated device

ABSTRACT

An integrated device includes a configuration circuit that is coupled to first and second bond pads and first and second conductive paths of the integrated device. The circuit receives a map signal that has a first value during a first operational mode of the integrated device and a second value during a second operational mode of the integrated device. In response to the first value, the circuit couples the first pad to the second conductive path. In response to the second value, the circuit couples the first pad to the first conductive path and the second pad to the second conductive path. The first operational mode may be a wafer test mode.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a divisional of U.S. patent application Ser. No.08/619,261, filed Mar. 18, 1996, now U.S. Pat. No. 5,796,266 issued Aug.18, 1998.

TECHNICAL FIELD

The present invention relates generally to electronic devices, and morespecifically, to a circuit for dynamically configuring bond-padconnections for different operational modes of an integrated circuit.

BACKGROUND OF THE INVENTION

Referring to FIG. 1, one or more dies 2 are formed in a conventionalmanner on a wafer 4, which is formed from a semiconductor material suchas silicon. The dies 2 are integrated circuits or devices that have beenformed, but have not been detached from the wafer 4. For clarity, onlyone row of dies 2 is shown, but will be understood that generallymultiple rows of dies 2 are formed to substantially fill the surface ofthe wafer 4. During a wafer test procedure, conventional apparatus (notshown) electrically tests the dies 2. The testing apparatus includesprobes that contact selected ones of the bond pads (not shown) of thedies 2.

A limitation associated with such a wafer test procedure is that eachbond pad that will receive a signal from the testing apparatus oftenmust be placed only along the sides 8 of the dies 2 in order to performsimultaneously testing of multiple dies 2. Because the dies 2 are placedrelatively close together along their sides 6 to maximize the area ofthe wafer 4 occupied by the dies 2, the bond pads that are located alongthe adjacent sides 6 are often inaccessible to the probes of the testingapparatus, particularly when all of the dies 2 on the wafer 4 are testedsimultaneously. That is, the probes of the testing apparatus can oftenonly contact the accessible bond pads that are located along the othersides 8 of the dies 2. (The dies 2 are typically formed in the wafer 4such that there is sufficient clearance for the test probes to accessthe sides 8 of each of the dies 2.) Requiring the bond pads that areused during the wafer test procedure to be located only along the sides8 may cause inefficient and complex circuit layouts on and increase theareas of the dies 2.

Referring to FIG. 2, which shows a top view of a die 2 of FIG. 1, aknown solution to this limitation is discussed. For clarity, the wafer 4and the remaining dies 2 of FIG. 1 are omitted from FIG. 2. The die 2includes accessible test pads 10 and accessible bond pads 14, which arelocated along accessible sides 8, and inaccessible pads 12, which arelocated along inaccessible sides 6. For clarity, FIG. 2 shows only twotest pads 10a and 10b, two inaccessible bond pads 12a and 12b, and twoaccessible bond pads 14a and 14b, it being understood that the die 2 mayinclude more or less of each of these pads. Each test pad 10 iselectrically coupled to circuitry (not shown) that is coupled to acorresponding pad 12 and that is to receive a signal from the testingapparatus during a wafer test procedure. Thus, by physically accessingtest pads 10, the testing apparatus can electrically access thecircuitry that is coupled to the inaccessible pads 12. Once the test iscomplete, however, the pads 10 typically serve no further purpose.

A limitation of this known solution is that the length of the accessiblesides 8 must be sufficient to accommodate the required number of thepads 14 and the test pads 10. Thus, the test pads 10 often increase thelength of the sides 8, and thus often increase the area of the die 2.

SUMMARY OF THE INVENTION

In accordance with an aspect of the present invention, an integratedcircuit is provided. The integrated device includes a circuit that iscoupled to first and second bond pads and first and second conductivepaths of the integrated device. The circuit receives a map signal thathas a first value during a first operational mode of the integrateddevice and a second value during a second operational mode of theintegrated device. In response to the first value, the circuit couplesthe first pad to the second conductive path. In response to the secondvalue, the circuit couples the first pad to the first conductive pathand the second pad to the second conductive path.

An advantage provided by one aspect of the invention is a reduction inthe number of test pads required in a die.

An advantage provided by another aspect of the invention is a reductionin the area of a die.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a top plan view of a semiconductor wafer having dies formedthereon as is known in the art.

FIG. 2 is a top plan view of a die of FIG. 1.

FIG. 3 is a top plan view of a die formed in accordance with the presentinvention.

FIG. 4 is a block diagram of one embodiment of the configuration circuitof FIG. 3.

FIG. 5 is a schematic diagram of one embodiment of the configurationcircuit of FIG. 4.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 3 is a top plan view of a die 16 that is formed in accordance withthe present invention. For clarity, the wafer in which the die 16 isformed, and the other dies formed in the wafer, are omitted. The die 16includes sides 8, which are accessible to a testing apparatus (notshown), and sides 6, which are substantially inaccessible to the testingapparatus during certain testing procedures, such as simultaneoustesting of multiple dies 2. One or more bond pads 12 and 14 are locatedalong the sides 6 and 8, respectively. For clarity, FIG. 3 shows onlyone inaccessible pad 12 and one accessible pad 14. A conventionalcircuit B is coupled to the pad 12 while the circuitry of the die 16 isin a first or normal mode of operation. In order to test the circuit B,a test signal must be applied to the circuit B. However, the pad 12 thatis coupled to the circuit B is inaccessible and thus cannot be used toapply the test signal to the circuit B. A conventional circuit A iscoupled to the pad 14. The circuit A is of the type that either need notbe tested or need not be tested at the same time that the circuit B isbeing tested. Since the pad 14 is not needed by the circuit A during thetesting of the circuit B, the pad 14 can be temporarily connected to thecircuit B during a testing procedure while the circuitry of the die 16is in a second or test mode of operation to allow test signals to beapplied to the circuit B. (For purposes of the invention, the details ofthe structure and operation of the circuits A and B are unimportant andtherefore these circuits are not discussed in detail.) The pad 14 cannotbe omitted from the die 16, however, because it is used in the first andother operating modes of the integrated circuit formed on the die 16. Aconfiguration circuit 18, described in detail below, is used to connectthe pad 14 to the circuit B during the test mode for the circuit B.

The operation of the configuration circuit 18 is controlled by aconfiguration or map signal, a configure or map pad 20 to which the mapsignal is applied by external means. The map pad 20, which may besimilar in size and construction to the known test pads 10 (FIG. 2), isdisposed along one of the accessible sides 8.

In operation during testing of the die 16, the test apparatus drives themap pad 20 with a configure or map signal. In response to this mapsignal, the configuration circuit 18 couples or maps the unused pad 14to the circuit B, which is normally driven by signals that are appliedto the used pad 12. That is, the circuit 18 configures the connectionsof the pads 12 and 14 so that the testing apparatus can drive thecircuit B via the accessible but unused pad 14. Therefore, by using onemap pad 20 and one or more unused pads 14, one can reduce the number ofor eliminate altogether the test pads 10 (FIG. 2), and thus reduce thearea of the die 16 as compared with that of known dies.

FIG. 4 is a block diagram of one embodiment of the configuration circuit18 of FIG. 3. The circuit 18 includes a first mapping or switchingcircuit 22 that has a first signal terminal coupled to a referencevoltage V_(REF), a second signal terminal coupled to the accessible butunused pad 14, a first control terminal coupled to the map pad 20, asecond control terminal coupled to an enable signal generator, here apad 21, that provides a signal ENABLE, and a third signal terminalcoupled to a conductive path or signal conductive path A. The signalconductive path A is also coupled to the conventional circuit A. The barover ENABLE indicates that it is active at a low logic level, i.e.,logic 0. The circuit 18 also includes a second mapping or switchingcircuit 24 that has a first signal terminal coupled to the pad 14, asecond signal terminal coupled to the inaccessible but used pad 12, afirst control terminal coupled to the map pad 20, a second controlterminal coupled to the enable pad 21, and a third signal terminalcoupled to a conductive path or signal conductive path B. The signalconductive path B is also coupled to the conventional circuit B.

In operation, during the first or normal operational mode of theintegrated circuit on the die 16, the circuit 18 couples the pad 12 tothe circuit B and couples the pad 14 to the circuit A. The pad 20 isdriven with a first logic level to indicate this first mode ofoperation. Because many or all of the first and other nonwafer-testoperational modes are implemented after the die 16 has been packaged,and because one often lacks access to the pads 20 and 21 after the die16 is packaged, map signal and enable signal generator circuits (notshown) are often formed on the die 16 to drive the pad 20 with the mapsignal and the pad 21 with ENABLE. An example of such generatorsincludes conventional pull-up or pull-down resistors or latches. If suchgenerators are used, the map pad 20 and the enable pad 21 may beeliminated, and the map signal and enable signal generators may bedirectly coupled to the appropriate internal nodes. When present anddriven externally, the map pad 20 and the enable pad 21 may beconsidered the map signal and enable signal generators, respectively.For example purposes, it is assumed that the map pad 20 and the enablepad 21 are present. In response to this first logic level and a logic 0for ENABLE, the first mapping circuit 22 couples the pad 14 to thecircuit A via the signal conductive path A, and the second mappingcircuit 24 couples the pad 12 to the circuit B via the signal conductivepath B.

In operation, the second or wafer-test procedure of the integratedcircuit is entered by the testing apparatus driving the pad 20 to asecond logic level, and driving the ENABLE signal to a logic 0. Thefirst mapping circuit 22 then decouples the pad 14 from the conductivepath A, and drives the conductive path A with a fixed voltage V_(REF),which in one embodiment of the invention is a logic level. Also inresponse to the second logic level and ENABLE, the second mappingcircuit 24 couples the pad 14 to the circuit B via the conductive pathB. The second mapping circuit 24 may also decouple the pad 12 from theconductive path B, and thus from the circuit B, although such decouplingis often unnecessary. Thus, in the test mode of operation, the testingapparatus can drive the circuit B, which is driven by pad 12 in thefirst mode of operation, by driving the unused but accessible pad 14whenever ENABLE is logic 0.

FIG. 5 is a schematic diagram of one embodiment of the configurationcircuit 18 of FIG. 4. As shown, the first mapping circuit 22 includes aninverter 26 that has an output and an input coupled to the pad 20 forreceiving a signal MAP. A NAND gate 28 has a first input coupled to theoutput of the inverter 26, a second input, and an output coupled to theconductive path A. The NAND gate 28 also has supply terminals that arecoupled to Vcc (logic 1) and ground (logic 0). Depending upon the logiclevel with which the first mapping circuit 22 drives conductive path Aduring a test mode, either Vcc or ground is used as V_(REF) (FIG. 4). Abuffer 29 has a signal input coupled to the pad 14, a control inputcoupled to ENABLE, and an output coupled to the second input of the NANDgate 28. Because only one buffer 29 buffers the signal from the pad 14,ENABLE is coupled to the buffer 29 instead of the first mapping circuit22 as shown in FIG. 4. It is understood, however, that one can makevarious modifications to the circuit of FIG. 5 such that ENABLE isdirectly coupled to the first mapping circuit 22 as shown in FIG. 4. Forexample, the circuit 18 could include a first buffer in the firstmapping circuit 22 and a second buffer in the second mapping circuit 24,where both of the buffers have signal inputs coupled to the pad 14 andcontrol inputs coupled to ENABLE.

The second mapping circuit 24 includes an inverter 30 that has an outputand an input coupled to ENABLE. A NAND gate 32 has a first input coupledto the output of the inverter 30, has a second input, and has an output.An inverter 34 has an input that is coupled to the pad 20, and has anoutput coupled to the second input of the NAND gate 32. An inverter 36has an input coupled to the pad 20 and has an output. An electronicswitch 38 has a signal input coupled to the output of the buffer 29, hasfirst and second complementary control inputs respectively coupled tothe input and the output of the inverter 36, and has an output coupledto the conductive path B. An inverter 40 has an input that is coupled tothe output of the inverter 34 and has an output. A buffer 42 has asignal input coupled to the pad 12, has a control input coupled to theoutput of the NAND gate 32, and has an output. An electronic switch 44has a signal input coupled to the output of the buffer 42, has first andsecond complementary control inputs respectively coupled to the inputand the output of the inverter 40, and has an output coupled to theconductive path B.

In operation during the first or normal mode of operation, the circuit18 couples the pad 12 to the signal conductive path B and couples thepad 14 to the signal conductive path A. MAP is driven to an inactivelogic 0, typically by a circuit (not shown) formed on the die 16, asdiscussed above in conjunction with FIG. 4. The inverter 26 converts thelogic 0 MAP to a logic 1 MAP, which enables the NAND gate 28. The NANDgate 28 then acts as an inverter, and couples the conductive path A tothe complement of the signal that drives the pad 14. Although not shown,the circuit A of FIG. 4 may include an inverter to generate the originalsignal on pad 14 from its complement on the conductive path A. The NANDgate 32, in response to the logic 1 MAP signal at one of its inputs andthe logic 1 at its other input, generates at its output a logic 0 thatenables the buffer 42. Furthermore, the logic 1 MAP signal and itscomplement, which the inverter 40 generates at its output, close theswitch 44 so that it couples the pad 12 to the conductive path B via thebuffer 42 whenever ENABLE is at logic 0. Finally, the logic 0 MAP, bothdirectly and through the inverter 36, disables the switch 38 to isolatethe pad 14 from conductive path B.

In operation during the second or test mode, the testing apparatusdrives the pad 20, and thus MAP, to an active logic 1. The inverter 26provides a logic 0 MAP to one of the inputs of the NAND gate 28, therebydisabling the NAND gate 28 so that conductive path A is driven with alogic 1 independently of the signal driving the pad 14. Thus, the NANDgate 28 decouples the pad 14 from the conductive path A, and holds theconductive path A at a substantially constant voltage V_(REF), which inthis embodiment is a logic 1 derived from Vcc. The logic 1 MAP via theinverter 34 causes the NAND gate 32 to output a logic 1 which disablesthe buffer 42. The pad 12 is then decoupled from any other portion ofthe circuit 18, including conductive path B to circuit B. The logic 0MAP, both directly and via the inverter 40, opens the electronic switch44. Thus, the switch 44 and the buffer 42 decouple the pad 12 from theconductive path B. Furthermore, the logic 1 MAP, both directly and viathe inverter 36, closes the switch 38, which thus couples the pad 14 tothe conductive path B via the buffer 29. Thus, during the second or testmode, the unused but accessible pad 14 is coupled to the conductive pathB, and effectively substitutes for the inaccessible pad 12 wheneverENABLE is at logic 0.

It will be appreciated that, although specific embodiments of theinvention have been described herein for purposes of illustration,various modifications may be made without departing from the spirit andscope of the invention. For example, although discussed with respect toconfiguring pad connections for normal and test operational modes, theinvention may be used to configure the pads for two or more other typesof operational modes with or without the use of a plurality of mapsignals. Also, although the circuit of FIG. 5 uses the configurationcircuit 18 to configure the pads 12, 14 as inputs to the circuits A andB, it will also be understood that the pads 12, 14 may also beconfigured as outputs of the circuits A and B. Accordingly, theinvention is not limited except as by the appended claims.

What is claimed is:
 1. A method for configuring pad connections in anintegrated circuit, comprising:coupling a first pad to a firstconductive path and a second pad to a second conductive path while saidintegrated circuit is in a first mode; and coupling said first pad tosaid second conductive path and holding said first conductive path at asubstantially constant potential while said integrated circuit is in asecond mode.
 2. The method of claim 1, further comprising decouplingsaid second pad from said second conductive path while said integratedcircuit is in said second mode.
 3. The method of claim 1, furthercomprising decoupling said first pad from said first conductive pathwhile said integrated circuit is in said second mode.
 4. A method forconfiguring pad connections in an integrated circuit, the integratedcircuit having first and second pads, and a configuration circuit, thefirst and second pads providing a respective signal to first and secondcircuits, respectively, while the integrated circuit is in a first mode,the integrated circuit being in the first mode in response to theconfiguration circuit receiving an inactive map signal and being in asecond mode in response to the configuration circuit receiving an activemap signal, the method comprising:receiving an active map signal; andswitching from the first signal pad to the second signal pad to providesignals to the first circuit while the integrated circuit is in thesecond mode.
 5. The method of claim 4 wherein switching compriseselectrically coupling the second signal pad to the first circuit andelectrically decoupling the first signal pad from the first circuit. 6.The method of claim 5 wherein coupling comprises closing a switchcoupled between the second signal pad and the first circuit, anddecoupling comprises opening a switch coupled between the first pad andthe first circuit.
 7. The method of claim 4, further comprisingproviding to the second circuit a constant voltage while the secondsignal pad provides signals to the first circuit.
 8. The method of claim7 wherein providing comprises coupling the second circuit to a constantvoltage source.
 9. The method of claim 5, further comprising decouplingthe second pad from the second circuit while the integrated circuit isin the second mode.
 10. A method of configuring signal pad connectionsin a configuration circuit of a integrated circuit, the configurationcircuit coupling a respective signal applied to first and second signalpads to first and second circuits, respectively, in response to theconfiguration circuit receiving an inactive map signal, the methodcomprising:coupling the signal applied to the first signal pad to thesecond circuit in response to the configuration circuit receiving anactive map signal.
 11. The method of claim 10, further comprisingdecoupling the second signal pad from the second circuit in response tothe configuration circuit receiving an active map signal.
 12. The methodof claim 11 wherein decoupling comprises opening a switch coupledbetween the second signal pad and the second circuit.
 13. The method ofclaim 10, further comprising driving the first circuit with a constantvoltage while the first signal pad is coupled to the second circuit. 14.The method of claim 13 wherein driving the first circuit comprisescoupling the first circuit to a constant voltage source.
 15. The methodof claim 13, further comprising decoupling the first signal pad from thefirst circuit while the first signal pad is coupled to the secondcircuit.